1. Field of the Invention
The present invention relates generally to a tape reel structure for a tape cassette. More specifically, the invention relates to a tape reel structure of a tape cassette with an improved reel flange supporting structure. Further particularly, the invention relates to a tape reel structure of a tape cassette with an inner cylindrical boss section and an outer cylindrical reel section coaxially arranged in a spaced apart relationship and connected by radially extending ribs.
2. Description of the Background Art
A magnetic tape cassette, such as a video tape cassette for a video tape recorder (VTR), has been disclosed in the Japanese Utility Model Second (examined) Publication (Jikko) Showa 57-56382. The disclosed magnetic tape cassette employs tape reels, each of which has upper and lower reel flanges. The tape reel also has coaxially arranged inner and outer sections in a spaced apart relationship to each other. The inner cylindrical section serves as a boss for drivingly receiving a reel shaft of an associated tape recording and/or reproducing apparatus. The outer cylindrical section forms a reel body so that a magnetic tape as a recording medium is wrapped or wound therearound. Radially extending ribs are provided so between the inner and outer cylindrical sections.
Such tape reels are formed of a synthetic resin by injection molding, in which molten resin is injected into molding dies. In this case, when the radially extending ribs extends through an overall length of the inner and outer cylindrical sections, flows of the molten resin injected through the radial center of the reel are formed so that the flows confluence at about the axial intermediate portion of the outer cylindrical section. Confluencing of the molten resin flows tends to form a wave on the outer periphery of the outer cylindrical section. That is, during the injection molding process, two molten resin flows are formed. The first resin flow flows radially through the portion of the die to form the lower reel flange. The second resin flow is formed to flow through the upper end wall of the portion for forming the upper end wall of the inner cylindrical section and through the upper end wall of the inner cylindrical section and through the upper end portion of the rib. Part of the resin in the first flow flows along the inner and outer cylindrical sections and the ribs toward the upper end. On the other hand, part of the molten resin in the second flow flows through the inner and outer cylindrical sections and the ribs toward the lower flange. Due to the opposite flow directions of the molten resin in the first and second flows confluencing at the axial intermediate portion, stress is created in the resin. This stress causes formation of a waving uneveness at the confluencing portion. When waving of the outer periphery of the outer cylindrical section is caused, wrinkles tend to be formed on the tape to cause disturbance of the signal or data to be recorded on the tape. Such disturbance of the recorded signal or data will cause a disturbance in the reproduced image in the case of a video tape.
Formation of waving uneveness on the outer periphery of the outer cylindrical section can be prevented by shortening the length of the rib so as to interrupt the second flow by discontinuous flow between the inner and outer cylindrical sections at the upper end thereof. In this case, however, another problem is encountered in resilient deformation at the discontinued portion of the outer cylindrical section toward the inner cylindrical section when the tape is tightly wound therearound. Namely, by shortening the ribs, an upper end portion of the outer cylindrical section becomes free from inward or radial bending. This causes radially inward bending of the portion where it is not restricted by the ribs. As a result of radially inward bending at the upper portion of the outer cylindrical section, the tape wound therearound may constantly be subjected to uneven force in a direction of the width thereof. When the stress exerted by the uneveness of the force in the transverse direction of the tape becomes significant, wrinkles may be formed on the tape to cause disturbance of the signal or data to be recorded on the tape.